The knowledge on the heterochromatin condensation state (HChCS) in central nuclear “gene rich” regions is limited although the heterochromatin reflects the gene silencing. Therefore, the HChCS in these regions was studied in proliferating granulocytic progenitors and terminally differentiated (mature) neutrophilic granulocytes. The HChCS was measured using computer assisted image optical densitometry at the single cell level. The bone marrow smears of patients with chronic myeloid leukemia represented a convenient model because of the increased number of progenitor and mature cells for density measurements. In addition, the heterochromatin density of central nuclear regions was also measured in myeloblasts of the K 562 cell lineage originated from the patient with that disease. The HChCS in central nuclear regions of both granulocytic progenitors and mature granulocytes was heterogeneous. The maximal and minimal density values were about 9-10 per cent above and below mean values in both myeloblasts and mature granulocytes. The heavy condensed heterochromatin of central nuclear region might reflect the location of silent genes during the whole granulocytic development. In contrary, the less condensed heterochromatin structures in central nuclear regions of granulocytic progenitors and mature granulocytes might just represent foci with the potential for the gene activation regardless of the differentiation and maturation stage. The HChCS in central nuclear regions was larger in small nuclear segments of mature granulocytes than in large nuclei of their progenitors. The HChCS was also increased in apoptotic K 562 myeloblasts with the decreased nuclear diameter. Such phenomena opened an “old - new” question on mutual relationship between the reduced nuclear size and the HChCS.

Institute of Hematolohy and Blood Transfusion Prague

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